System CPU Usage

Posted on 2006-05-12
Last Modified: 2010-04-14
What does the System CPU usage mean?

I recently downloaded a widget for my dashboard that monitors CPU usage. I was surprised to find that most of the time the CPU usage was right up at 100% being split about 40-60 between "User" and "System" respectively with 0-2% designated as "Idle". Does this mean that my processor is maxing out all the time? I have a 1.33 GHz PowerPC G4 with 1GB DDR SDRAM, and it seems to be running fine.

I would have expected to see most of my CPU usage percentage being designated as idle, as I can't imagine I am using more than 40% very often. What does it mean when it says that "System" is taking up most of my CPU power?
Question by:jfredrickson
    LVL 23

    Expert Comment

    Mac OS X 10.4 Spotlight indexer runs in the background.  If you have rapidly changing files in the file system (or a freshly mounted filesystem that has not been indexed yet), Spotlight will be doing its job in the background.  Safari, too, can consume copious CPU time - usually animating large numbers of ads [thank heaven for Pith Helmet].

    You can see what processes are consuming CPU cycles by running the command 'top' from the command line, or the GUI version, "/Applications/Utilities/Activity"

    LVL 4

    Author Comment

    So when the "User" and "System" usage is up near 100% it means that the processor is actually being used 100%? Why am I not then seeing any real slowdown in application speed?
    LVL 23

    Accepted Solution

    Background processes use CPU resources when the system is not doing anything else.  They yield the CPU to the foreground processes when you use the keyboard or mouse.
    LVL 4

    Author Comment

    Ahh, that makes sense. What a genius design :)

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